1. Field of the Invention
The present invention relates to a resist composition and, more particularly, to a chemically-amplified resist composition that contains a novel polymer.
2. Description of Related Art
As the integration level of the semiconductor integrated circuits (ICs) rapidly increases, the line width required for the lithography technique becomes smaller and smaller. Theoretically, the smaller the wavelength of the light source, or the bigger the numerical aperture (NA) of the optics system, the better the resolution of the pattern made by lithographic process will be. Due to the design rule of the ICs for the mass production of 1 G byte DRAM, it is necessary for manufacturers to advance research in the 0.13 μm lithographic process. However, the KrF (248 nm) excimer laser currently used is no longer competent to facilitate the processes under 0.13 μm. As a result, the ArF (193 nm) excimer laser has become the essential device in this field.
Currently, the most promising technique for advancing development in the 0.09 μm (90 nm) lithographic process is the ArF lithographic process utilizing chemically-amplified resists. Nevertheless, the 193 nm resists need to meet the properties of high resolution, long depth of focus (DOF) and process window, good thermal stability and adhesion, high sensitivity (<5 mj/cm2), excellent resistance to plasma etching, moderate rate of dissolution, and being compatible to the standard chemicals used for IC production, such as the 2.38% TMAH developer.
In the early days of research of the 193 nm resist, the focus was mainly on acrylic polymer. In order to improve the polymer's resistance against etching and hydrophilicity, many polymers having cyclic structure, such as Cyclo-Olefin-co-Maleic Anhydride (referred to as COMA hereinafter), Cyclo-Olefin Copolymer (referred to as COC hereinafter), and Cyclo-Olefin-co-Maleic anhydride-co-acrylate were developed. However, those polymers mentioned above are not easy to be synthesized. For example, the synthesis has to be catalyzed by rare elements like transition metals. After the synthesis, it is hard to remove the metallic ions from the synthesized polymer. Besides, the synthesized products have excessively high absorbance and poor hydrophilicity so it is still necessary to develop a new polymer from which the foregoing disadvantages are absent.
Vinyl Ether-Maleic Anhydride copolymer (referred to as VEMA hereinafter) has the advantages that it can overcome the drawbacks of those co-polymers above-mentioned. For example, VEMA can be synthesized by using a much easier method of radial polymerization; the resist made by VEMA has excellent adhesion to the substrates; and it has better resistance against etching than the acrylates, and lower absorbance than norbornene-series polymers.
In recent years, some VEMA-related literature has been published. Firstly, the structure of VEMA polymer was proposed in Proceedings of SPIE, 3999, 54-61 by Sang-Jun Choi et al. (2000). That publication combined Maleic anhydride, acid-labile acrylates, and linear alkyl vinyl ether or cyclic vinyl ether compounds such as 3,4-dihydro-2H-pyran (DHP) or 3,4-dihydro-2-ethoxy-2H-pyran (DHEP) to form a co-polymer.
George G. Barclay et al. disclosed in U.S. Pat. No. 6,306,554 a polymer with a similar structure to that of Sang-Jun Choi. A norbornene was added to adjust the properties of the polymer. In addition to DHEP, the vinyl ether disclosed in the patent further includes cyclic vinyl ether compounds such as 3,4-dihydro-2-mthoxy-2H-pyran (DHMP). Preferably, the molecular weight of this kind of high polymer ranges from 2,000 to 20,000, the polymerization-dispersion degree is about or less than 2, and the molar ratio of the acid-labile acrylate to the high polymer is from 40 to 60%.
Nevertheless, the VEMA polymer disclosed above is not satisfactory because it uses a vinyl ether compound with cycloalkyl-substituted main chain, which results in poorer polymerization activity than that which uses a vinyl ether compound with cycloalkyl substituted at side-chain. Therefore, the polymer has a lower uniformity in the compositions of chain structure, low synthesis yield and molecular weight, higher degree of polymerization-dispersion, and a more complex synthesizing reaction. Particularly, introducing another norbornene made the degree difficulty of synthesis rise, as well as being difficult to control.
Although vinyl ether having a linear substituent at side chain can get a polymer with high uniformity of chain composition, high synthesis yield and molecular weight, and narrow degree of polymerization-dispersion, its resistance against etching is too weak. The present invention uses vinyl ether with a cycloalkyl substituent at a side chain that has both good activity and etching resistance, Maleic anhydride, and acid-labile acrylates to build a polymer with excellent reaction activity and resistance against etching.
Reppe et al. first synthesized vinyl ether in 1956. Alcohol was allowed to react with acetylene under high pressure (20˜50 atm) and high temperature (180-200° C.), and catalyzed by potassium hydroxide or organic metal catalyst, e.g., Y. Okimoto et al. (2002) in J. Am. Chem. Soc., 124, 1590. However, B. A. Trofimov et al. (2000) disclosed a more moderate reaction condition in Synthesis, 11, 1521 that involved dissolving alcohol and potassium hydroxide in DMSO followed by reacting with acetylene to synthesize certain kinds of vinyl ether compounds.
The present invention discloses compositions of VEMA polymer, which must not contain more than 40 molar percent of acid-labile acrylate like the prior art aforementioned, but can get better properties of hydrophilicity, adhesion, resistance against dry-etching, thermal properties, and transmittance by adjusting the percentage of acid-labile acrylates in the polymer, which makes the resists applied be more flexible.
The present invention further provides polymers, which are formed by introducing another acrylate with a cycloalkyl into the polymer aforementioned, which solves the problems that come about when introducing a norbornene and is easier to be synthesized and controlled. The acrylates with a cycloalkyl work well in adjusting the properties of the polymer in the resist. Adjusting the ratio of acrylates to acid-labile acrylates can regulate the hydrophilicity, adhesion, resistance against dry-etching, thermal property, and transmittance of the polymer, and then provides more flexible and more diverse techniques that can improve the properties of the polymer. As a result, the polymer makes lithographic process form images with better resolution, profile, and light-sensitivity.
The resist composition of the present invention has good hydrophilicity, adhesion, and resistance against dry etching, which improves the adherence between the resist and the substrate, enhances its shaping ability, and strengthens the resist pattern after being developed. Besides, the better hydrophilicity makes the developer solution disperse on the resist more uniformly, which results in good and uniformly resolved images.